Process for impregnating nonwovens with alkyl acrylate-carboxyl latices

ABSTRACT

A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength or delamination resistance and wet tensile strength, is provided. The nonwoven fabrics and papers are impregnated with an alkyl acrylate copolymer latex containing carboxyl functionality and exposed to ammonia or amine vapors prior to the drying and curing operations to obtain the improved properties. Papers treated in this manner have shown up to a two-fold increase in internal bond strength.

United States Patent 1191 Wheelock Feb. 19, 1974 [5 PROCESS FORIMPREGNATING 2,983,623 5 1961 Coates 117/62.2 NONWOVENS WITH ALKYL3,085,897 4/ 1963 Priest et al.... 117/62.2 2,429,698 10/1947 Schneider117/106 R ACRYLATE-CARBOXYL LATICES 3,168,415 2/1965 Goldstein et a1..117/62 [75] Inventor: George L. Wheelock, Avon Lake, 3,318,722 5/1967Ullman 117/62 Ohio 3,404,022 10/1968 Chance et aL 1l7/62.2 3,472,61110/1969 Langwell 117/62.1 Asslgneei The Goodrich p y, New 3,483,01412/1969 lssacs et a1 117/62 York, NY. [22] Filed; July 14, 1972 PrimaryExaminer-william D. Martin Assistant ExaminerM. Sofocleous PP N04271,972 Attorney, Agent, or Firm-J. Hughes Powell, Jr.

Related US. Application Data [63] Continuation-impart of Ser. No.725,152, April 29, [57] ABSTRACT 1968, abandoned. A process forobtaining nonwoven materials having I improved physical properties,especially internal bond [52] US. Cl. l17/62.2, 117/106 R, 117/140 A,strength or delamination resistance and wet tensile 117/155 UA strength,is provided. The nonwoven fabrics and pa- [51] Int. Cl B44d l/44, 844dl/48, B32b 29/00 pers are impregnated with an alkyl acrylate copolymer[53] Field of Search 117/62, 62.1, 62.2, 106 R, latex containingcarboxyl functionality and exposed to 117/140 A, 155 UA; 161/170 ammoniaor amine vapors prior to the drying and curing operations to obtain theimproved properties. Pa- [56] References Cited pers treated in thismanner have shown up to a twofold increase in internal bond strength.

10 Claims, No Drawings PROCESS FOR IMPREGNATING NONWOVENS WITH ALKYLACRYLATE-CARBOXYL LATICES CROSS REFERENCE TO RELATED APPLICATION This isa continuation-in-part of my copending application Ser. No. 725,152,filed Apr. 29, 1968, now abandoned.

BACKGROUND OF THE INVENTION Nonwoven fibrous materials, typically formedby randomly depositing individual fibers to form a web and thenimpregnating the web with a binder to hold the individual fiberstogether, are recognized as possessing many advantages over conventionalwoven materials. Such advantages include absence of raveling, smoothersurfaces, increased softness, improved hand, greater absorbency, higherloft, and others. Underlying these advantages is the fact that, unlikewoven materials which owe their physical characteristics primarily tothe construction of the weave and are thereby limited for a given fiber,the properties and characteristics of the nonwoven fabrics may be variedover a wide range with the same fiber simply by varying the bondingagent (binder).

Although the particular fiber/binder combination and web-type willgovern the ultimate physical properties achievable in a nonwoven fabric,the amount of binder taken up by the nonwoven substrate and theuniformity with which the binding agent is dispersed throughout thenonwoven will also be important factors in achieving the optimumproperties. If the nonwoven substrate as a whole is deficient in bondingagent or if localized areas are deficient, the physical properties suchas wet and dry tensile strengths and especially the internal bondstrength (resistance to delamination or splitting) are markedly reduced,in fact, the nonwoven is often rendered useless. This problem ofobtaining adequate binder content throughout the nonwoven material isespecially significant when using the aqueous emulsion binder systems.These are probably the single most important class of binder becausethey not only provide nonwoven fabrics having excellent physicalproperties and wear endurance but also, as a practical matter, they areeasily applied to the nonwoven substrate by the use of conventionalsaturation and spraying techniques. It is sometimes so difficult withthese emulsion systems to incorporate sufficient binder to obtain thedesired level of physical properties for certain nonwoven applications,that it becomes necessary to resaturate the nonwoven with latex afterdrying the first binder solution; but this is not a desirable method.

Efforts to overcome the problem of achieving an acceptable bindercontent has led to much work, primarily directed to obtaining moreefficient latices, that is, improved latex binder systems which permitthe use of less bonding agent to develop optimum physical properties inthe nonwoven material. Typically, these improved latex binders containreactive monomers, capable of reacting upon the application of heat,catalysis or other chemical reagents, to form cross-linked polymers.

This approach is not completely satisfactory either since the binders,even though more efficient, are still susceptible to migration throughthe nonwoven material. During the drying operation, polymeric binder canmigrate to the surface of the nonwoven material with the water andemulsifying agent resulting in a nonuniform distribution of the binderand lowered physical properties. The viscosity of the binder latex canbe increased prior to saturation by the addition of thickening agentssuch as natural gums and pastes, polyvinyl alcohol, and the like, toreduce the tendency of the binder to migrate within the nonwovenmaterial, however, this technique is only partially effective and makesit impossible to achieve uniform saturation of the nonwoven.

SUMMARY OF THE INVENTION I have now developed a process whereby nonwovenmaterials having markedly improved internal bond strength and resistanceto delamination are obtained. In most instances the wet tensile strengthof the nonwoven will also be noticeably increased. To obtain theseimproved properties, the nonwoven web or mat is impregnated with analkyl acrylate polymer latex containing carboxyl functionality which forthe purposes of the present invention can be obtained byinterpolymerizin g or overpolymerizing a carboxyl-containing monomer,preferably an afi-olefinically unsaturated carboxylic acid, with thealkyl acrylate. The saturated fabric or paper is then exposed to vaporsof ammonia or an amine prior to the drying operation.

The nonwoven materials, both fabrics and papers, 0- tained by thepresent process will have markedly increased internal bond strength anddelamination resistance over conventionally prepared nonwovens withoutthe ammonia or amine exposure. Resistance to delamination has beenincreased as much as 100 percent for some papers. The present processenables us to achieve a more uniform distribution of the binder withinthe finished nonwoven due to the ammonia or amine exposure prior to heattreatment. It is felt that the in situ thickening of the latex binderprior to the drying step reduces the migration of the polymer toward thesurface of the nonwoven as the water is removed during drying.

DETAILED DESCRIPTION The process of the present invention is applicableto any nonwoven material, that is, the particular fiber used in themake-up of the nonwoven and the thickness of the nonwoven does not limitthe application of the present process. This is not to say that certainfibers are not more useful for certain nonwoven applications thanothers, but only that if a fiber has the required specifications to beformed into a nonwoven web or mat then the nonwoven so formed may betreated according to the present process.

Natural fibers such as cotton, wool, silk, sisal, cantala, henequen,hemp, jute, kenaf, sunn and ramie may be used to form the nonwoven webor mat as well as synthetic fibers or filaments. Useful synthetic fibersin clude: rayon (viscose); cellulose esters such as cellulose acetateand cellulose triacetate; proteinaceous fibers such as thosemanufactured from casein; polyamides (nylons) such as those derived fromthe condensation of adipic acid and hexamethylenediamine or theselfcondensation of caprolactam; polyesters such as polyethylene glycolterephthalate; acrylic fibers containing a minimum of about percentacrylonitrile with vinyl chloride, vinyl acetate, vinyl pyridene,methacrylonitrile or the like and the so-called modacrylic fiberscontaining smaller amounts of acrylonitrile; fibers of copolymers ofvinyl chloride with vinyl acetate or vinylidene chloride; fibersobtained from the formal derivatives of polyvinyl alcohol; olefin fiberssuch as polyethylene and polypropylene; and the like.

The process of the present invention is particularly advantageous foruse with specialty papers which require the saturation of the paper matwith binders in order to modify the structural properties of the paper.Papers obtained from bleached or nonbleached pulp may be employed; also,those obtained by the unbleached sulfite, bleached sulfite, unbleachedsulfate (kraft), semibleached and bleached sulfate processes. Papersprepared wholly from synthetic fibers and those obtained from blends ofnatural cellulose and synthetic fibers also may be used.

The nonwoven mat or web may be formed by conventional techniques. Forexample, for papers they will be formed on a moving fine wire screenfrom an aqueous suspension of the fibers. When other fibers are to beformed into a nonwoven, depending on the particular fiber or fiber blendbeing used, whether the fibers are to be orientated or deposited atrandom, the thickness of the nonwoven, etc., the fibrous web can beformed by carding, garnetting, deposition from an air stream, depositionfrom solution, deposition from a melt, wet-laying, or the like.

The binders employed for the process of the present invention areaqueous carboxyl-containing dispersions of lower alkyl acrylatepolymers. The required carboxyl functionality may be either chemicallybound to the alkyl acrylate polymer, that is, one or morea,B-olefinically unsaturated carboxylic acid monomers will beinterpolymerized with the alkyl acrylate monomers or overpolymerized orgrafted on the alkyl acrylate base polymer; or physically admixed withthe alkyl acrylate polymer, for example, by the addition of a polymericcarboxylcontaining thickening agent to the alkyl acrylate polymer latex.In either case the carboxyl group will constitute from about 0.05 toabout 25 percent by weight of the total make-up of the polymeric binder.

The alkyl acrylate polymer binder latices employed are obtained bypolymerizing esters of a,B-olefinically unsaturated carboxylic acidshaving the structural formula wherein R is hydrogen, methyl or ethylgroup and R represents a hydrocarbon radical containing from one to 12carbon atoms. Representative monomers of the foregoing type includemethyl acrylate, ethyl acrylate, the propyl acrylates, the butylacrylates, the amyl acrylates, the hexyl acrylates, cyclohexyl acrylate,phenyl acrylate, 2-methylhexyl acrylate, n -octy1 acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-octylmethacrylate, dodecyl methacrylate and the like. Most preferred are thelower alkyl esters of acrylic and methacrylic acid containing from fourto carbon atoms.

The polymeric acrylate binders may contain one or more otherpolymerizable comonomers, preferably vinylidene monomers containing atleast one terminal group, interpolymerized with the alkyl acrylatemonomers. Such polymerizable comonomers may constitute up to about 49.95percent by weight of the polymer. Such polymerizable comonomers includethe conjugated dienes such as butadiene and isoprene; a-olefins such asethylene, propylene and isobutylene', vinyl aromatics such as styrene,a-methyl styrene, chlorostyrene, vinyl toluene and vinyl naphthalene,vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride,vinylidene chloride and vinylidene fluoride; vinyl esters such as vinylacetate; alkyl vinyl ethers such as methyl vinyl ether, isopropyl vinylether, n-butyl vinyl ether, isopropyl vinyl ether and haloalkyl vinylethers as 2- chloroethyl vinyl ether; nitriles as acrylonitrile ormethacrylonitrile; vinyl ketones and haloalkyl vinyl ketones;a,B-olefinically unsaturated amides such as acrylamide, N-methylacrylamide, N-t-butyl acrylamide, N- cyclohexyl acrylamide,methacrylamide, N-ethyl methacrylamide and diacetone acrylamide;a,B-olefinically unsaturated N-alkylol amides having the structuralformula wherein R is a hydrogen or an alkyl group containing from one tofour carbon atoms and x is a number from l to 4, such as N-methylolacrylamide, N-ethanol acrylamide, N-propanol .acrylamide, N-methylolmethacrylamide, and N-ethylol methacrylamide; polyunsaturated compoundssuch as methylene-bis-acrylamide, ethylene glycol dimethacrylate,diethylene glycol diacrylate, allyl pentaerithritol and divinyl benzene;alkoxyalkyl acrylates as ethoxyethyl acrylate, haloalkyl and cyanoalkylacrylates, excluding aminoacrylates and methacrylates; allylchloroacetate, vinyl chloroacetate; and the like as is known by thoseskilled in the art.

The carboxyl functionality present in the polymeric acrylate latexbinders useful in this invention is introduced by the use of one or morea,B-olefinically unsaturated carboxylic acid monomers containing fromthree to 10 carbon atoms. Representative examples of such acid monomersinclude acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylicacid, a-cyanoacrylic acid, crotonic acid, B-acryloxy propionic acid,hydrosorbic acid, sorbic acid, a-chlorosorbic acid, cinnamic acid,,B-styrylacrylic acid, itaconic acid, citraconic acid, maleic acid,fuman'c acid, mesaconic acid, glutaconic acid, aconitic acid and thelike. The preferred acid monomers are the a,B-monoolefinicallyunsaturated monocarboxylic acids such as acrylic acid and methacrylicacid. Mixtures of one or more of the above-mentioned carboxylic monomersmay be employed if desired. As was previously mentioned, the

The carboxyl-containing polyacrylate binders which containcarboxyl-containing monomers interpolymerized may be prepared by any ofthe conventional emulsion polymerization techniques. About 50 to 99.95percent of one or more of the above-mentioned alkyl esters ofa,B-olefinically unsaturated carboxylic acids will be interpolymerizedwith about 0.05 to 25 percent by weight of the a,B-olefinicallyunsaturated carboxylic acid monomer to constitute the polyacrylatelatices. In addition, up to about 49.5 percent by weight of otherpolymerizable vinylidene comonomers free of amine groups can beinterpolymerized therewith. The preferred polyacrylate binders usefulfor the present process will contain about 70 to 95 percent by weight ofthe acrylate ester, about 0.1 to percent by weight of thecarboxyl-containing monomers and about 5 to 29 percent by weight ofother polymerizable comonomers.

The aqueous medium may be emulsifier free or it may contain a surfaceactive agent. When an emulsifier is used to prepare the polyacrylatebinders it may range from as low as about 0.01 up to about 6 percent ormore as 8 to 10 percent by weight based on the total monomers. Theemulsifier may be charged at the outset of the polymerization or may beadded incrementally or by proportioning throughout the run. Any of thegeneral types of anionic or nonionic emulsifiers may be employed,however, best results are generally obtained when anionic emulsifiersare used. Typical anionic emulsifiers which may be used include thealkali metal or ammonium salts of the sulfates of alcohols containingfrom eight to 18 carbon atoms such as, for example, sodium laurylsulfate; alkali metal and ammonium salts of sulfonated petroleum orparaffin oils; sodium salts of aromatic sulfonic acids such asdodecane-l-sulfonic acid and octadiene-l-sulfonic acid; aralkylsulfonates such as sodium isopropyl benzene sulfonate and sodium dodecylbenzene sulfonate; alkali metal and ammonium salts of sulfonateddicarboxylic acid esters such as sodium dioctyl sulfosuccinate anddisodium N- octadecyl sulfosuccinamate; alkali metal or ammonium saltsof the free acids of complex organic monoand diphosphate esters; and thelike. So-called nonionic emulsifiers are octylor nonylphenylpolyethoxyethanol and the like. Preferred as emulsifiers are the alkalimetal salts of the aromatic sulfonic acids and the sodium salts of thearalkyl sulfonates of the formula wherein R is alkyl or alkenyl, havingeight to 20 carbon atoms such as octyl, decyl, dodecyl, alkoxy or ethoxygroups, or aryl, such as a phenyl radical of the formula wherein R is Hor an aliphatic radical containing one to 16 carbon atoms as the butyl,decyl, dodecyl and like alkyl or alkenyl radicals, y is CH or O, andnaphthyl Ar is benzyl or naphthyl and M is an alkali metal or NH Inaddition to the above-mentioned emulsifiers it may be desirable andadvantageous to add post-polymerization emulsifiers and stabilizers tothe polymeric latex binders in order to improve the latex stability ifit is to be stored for prolonged periods prior to use. Suchpost-polymerization emulsifiers may be the same as, or different than,the emulsifier employed in conducting the polymerization, preferablyanionic or nonionic agents.

To initiate the polymerization free radical catalysts are employed. Theuse of such catalysts, although in certain systems not absolutelyessential, insure a more uniform and controllable polymerization and asatisfactory polymerization rate. Commonly used free radical initiatorsinclude the various peroxygen compounds such as the persulfates, benzoylperoxide, t-butyl hydroperoxide, and l-hydroxycyclohexyl hydroperoxide;azo compounds such as azodiisobutyronitrile, and dimethylazodiisobutyrate; and the like. Especially useful as polymerizationinitiators are the water-soluble peroxygen compounds such as hydrogenperoxide and the sodium, potassium and ammonium persulfates.

The alkali metal and ammonium persulfate catalysts may be employed bythemselves or in activated redox systems. Typical redox systems includethe persulfates in combination with: a reducing substance such as apolyhydroxyl phenol and an oxidizable sulfur compound such as sodiumsulfite or sodium bisulfite, a reducing sugar, a diazomercapto compound,a ferricyanide compound, dimethylaminopropionitrile and the like. Heavymetal ions such as silver, cupric, iron, cobalt, nickel and others mayalso be used to activate persulfate catalyzed polymerizations. Ingeneral the amount of free radical initiator employed will range betweenabout 0.1 to 5 percent based on the weight of the total monomers. Theinitiator is generally completely charged at the start of thepolymerization, however, incremental addition or proportioning of theinitiator throughout the polymerization is often desirable.

In conducting the polymerization for the preparation of the acrylatebinder latices of the present invention the monomers are typicallycharged into the polymerization reactor which contains the water and theemulsifying agent. The reactor and its contents are then heated and thepolymerization initiator added. The temperature at which thepolymerization is conducted is not critical and may range from about 30C. to about 100 C. or higher. Excellent results, however, have beenobtained when the polymerization temperature is maintained between 0 andC. A pH below 7 is generally maintained throughout the polymerization.Polymerization modifiers such as the primary, secondary and tertiarymercaptans, buffers, electrolytes and the like may also be included inthe polymerization.

Preferred carboxyl-containing polyacrylate latices which have provedparticularly advantageous as binders for treatment by the process of thepresent invention are those having about 0.1 to 10 percent by weight ofthe a,B-olefinically unsaturated carboxylic acid monomer overpolymerizedon an alkyl acrylate base polymer. The base polymers will typicallycontain about 50 to 99.9 percent by weight based on the total monomersof an ester of an a,B-olefinically unsaturated carboxylic acid and fromabout zero to 49 percent by weight of one or more other aminefreepolymerizable comonomers, preferably from about 0.5 to 15 percent byweight of an a,,B-olef1nically unsaturated N-alkylol amide or 0.5 to 35percent by weight of an acrylic amide or nitrile such as'acrylamide,methacrylamide, acrylonitrile or methacrylonitrile.

These preferred and highly efficient overpolymerized polyacrylatelatices are obtained with slight modification of the conventionalpolymerization techniques described above. The acrylate base polymer isin fact formed using these conventional techniques.

In conducting the overpolymerization certain changes must be made.Generally, the carboxyl containing monomer may be overpolymerized byitself, or other polymerizable monomers can be combined with thecarboxyl-containing monomer. Useful polymers are obtained when the otherpolyrnerizable monomers are vinylidene monomers employed in amounts sothat the weight ratio of the vinylidene comonomer to the acid monomer isless than about 5:1. Excellent overpolymerizations are obtained when thevinylidene comonomer to acid monomer weight ratio is maintained at 1:1or below.

The same monomers interpolymerized to form the polyacrylate basepolymer, also serve as useful comonomers with the acid monomer in theoverpolymerization step. Small amounts of alkyl acrylates, such as ethylacrylate and methyl acrylate, have been found especially usefulcomonomers to be overpolymerized with the acid monomers. In addition tothe usual vinylidene comonomers, small amounts of polyfunctionalcompounds such as methylene-bis-acrylamide, ethylene glycoldimethacrylate, diethylene glycol diacrylate, allyl pentaerythritol,divinyl benzene and the like may also be included in theoverpolymerization. By including these vinylidene monomers andpolyfunctional compounds capable of cross-linking with the acid monomersduring the overpolymerization, latices having excellent stability andcapable of developing extremely high viscosities are obtained, whichwhen employed as binders for nonwovens according to the present process,provide nonwovens having much improved internal bond strength ordelamination resistance.

The overpolymerization or grafting of the acid monomers is commencedwhen the polymerization of the base polymer is complete or essentiallyso. More conveniently it is begun after about 50 percent conversion ofthe base monomers has been achieved. Preferably, the overpolymerizationis delayed until about 70 percent or more of the monomers comprising thebase polymer are polymerized. The technique of combining other monomerswith the carboxylic monomer is especially useful to obtain stableoverpolymerizations and latices when the overpolymerization is delayeduntil high conversions of the base monomers is achieved.

The present process consists of exposing the nonwoven material which hasbeen saturated with one of the above-mentioned carboxyl-containingpolymeric latex binders to the vapors of ammonia or amines. By suchexposure, the latex binder is thickened in situ, thereby reducing themigration of the polymeric binder from the interior regions of thenonwoven toward the surface as the water is removed during the dryingoperation. Thus, a more uniform distribution of the polymeric binderthroughout the nonwoven than was previously possible is achieved. Thenet result of such treatment is a noticeable improvement in the physicalproperties of the nonwoven material. The internal bond strength ordelamination resistance and generally the tensile strength, especiallythe wet tensile strength, of the nonwovens are increased by employingthe process of the present invention.

To achieve the maximum advantage of this invention, the pH of thecarboxyl-containing polymer latices must be maintained below specificlimits during the saturation or impregnation. This insures the completepenetration and uniformity of the binder latex throughout the nonwovenmaterial which is essential to obtain the improved physical properties.Although the pH requirement will vary from one latex to another,depending on the monomers employed and the carboxyl content, to beacceptable for impregnation the pH should preferably be maintained onthe acid-side. A neutral or slightly basic latex will give acceptableresults in most instances, however. In general, the pH of thecarboxylcontaining alkyl acrylate polymer latex will be maintained atabout 7.5 or below and more preferably between about 6.5 and 2.5.Excellent results are achieved when latices at the higher pH limits areacidified prior to saturation to achieve a more desirable pH andviscosity. To facilitate the saturation of the nonwoven, the totalsolids of the latex binder is generally maintained below about 50percent and excellent results are obtained with latices containing about15 to 35 percent total solids.

A critical feature of the present invention is the exposure of thesaturated nonwoven material to ammonia or amine vapors. Although ammoniais generally preferred due to its ready availability, gaseous nature andexcellent solubility in the binder latices at the temperatures employed,primary, secondary or tertiary aliphatic monoamines may also be employedto give excellent results. Typical amines which can be used may containup to 12 carbon atoms, however, amines containing up to six carbon atomsare generally preferred. Gaseous amines such as methyl amine, ethylamine, dimethyl amine and trimethyl amine have produced excellentresults. The higher molecular weight amines which are normally liquidsat room temperature, such as primary amines containing from three to l 1carbon atoms and the lower secondary and tertiary amines,

' which will normally exert an appreciable vapor pressure at roomtemperature, or slightly above, and are readily soluble in water mayalso be employed. Generally, the amines useful in the present processshould have boiling points less than about 150 C. and more preferablyless than C. The ready solubility of the ammonia and amines in waterinsures that binder latex even in the innermost regions of the nonwovenwill be uniformly acted on, thus rendering in situ thickening of thelatex to minimize subsequent binder migration. It is the ability of theammonia and amines to be instantaneously, or essentially so, taken up bythe saturated nonwoven and contact both the interior and surface regionswith the same effectiveness, which renders the present process so usefuland permits the development of superior physical properties in thenonwovens treated in accordance with the present invention.

Attempts to achieve thisuniform treatment of saturated nonwovens usingother techniques were unsuccessful. Either the binder could notuniformly penetrate the nonwoven in the cases where thickening of thebinder latex prior to saturation was employed, or when post-thickeningof the binder latex was attempted with agents other than the ammonia oramines of this invention, the initial thickening occurring at thesurface of the nonwoven is so pronounced and so rapid that it impedesfurther penetration of the thickening agent to the interior regions ofthe nonwoven and consequently EXAMPLE I To demonstrate the process ofthe present invention, a latex of an alkyl acrylate polymer having acarboxylthese interior regions are subject to migration of thecontaining monomer owl-polymerized was prepared hinder P y for use as abinder for nonwoven materials. The poly- Exposure of the saturatednonwoven material to the met latex was prepared by emulsion polymerizingin 4 ammonia of amine Vapors will depending on the parts watercontaining 0.26 part ammonium persulfate particular latex binder andthickening agent employed. and l ifi an l ifi d monomer mixture Contacttimes will generally be less than about 80 min- 10 prising 32 partswater, 35 parts ethyl acrylate, 2 7 utes, preferably they will rangebetween about 2 secparts l iu-il 1 8 n l id d 1 3 parts onds and 5minutes. With ammonia and the more vola- N ;h l 1 l id Th polymerizationwas tile amines, contact times between 5 seconds and l d d at 80 C, bmetering th monomer ixt re into minute have been Successfully p y andfound to the polymerizer for a period of about 1 hour. Near the impartmaximum Properties to the cured nonwoven completion of the metering amixture of 2.6 parts methmaterial. Once maximum thickening of the binderlatex li id 25 parts h l l ()3 part th l is achieved, additionalexposure to the ammonia or methacrylate d ()()5 part h l -bi l id amineswill Produce he further improvement in the was charged to the reactor.The polymerization was hehwoveh p Neither will any detrimental thenmaintained at 80 C. until essentially complete feets be realized fromProlonged exposure to the conversion was achieved. The total amount ofwater mehia amine Vapors, heweverand sodium lauryl sulfate emulsifierpresent in the final Exposure to the ammehla 0T amme ls convenientlylatex was 98 parts and 0.3 part respectively. The final brought about ina chamber maintained at room temlatex contained about 50 percent w] lidPemture or above, Such as a g y Oven, wherein a A saturation bath wasprepared by diluting the sufficient concentration Of the ammonia Oiamine vaearboxy]-eontaining acrylate latex to percent iota] P can hemaintained for Contact with the Saturated solids with water. 10 milsuncoated flat paper (Paterson nonwoven. Although the exposure ovens canbe mainparchment C h i a i i fib i0 fib tained at elevated temperatures,these temperatures Contact d supported i hi a Dacron marquisene shouldgenerally not exceed 212 F particularly if long velope was thensaturated by submerging the paper in I expesure times are p y Because ofthe Short the latex bath. The excess binder latex was removed by contacttimes possible with the present process, the satpassing the paperbetween padde queeze rolls main- "fated nonwoven y be continuouslyPassed through tained at 20 pounds pressure. The saturated paper was thegaseous ammonia or amine to facilitate the expoh v d fr m the mar isetreenvelope. sure step. Such a continuous process would be highly Paperssaturated in this manner were then exposed to desirable for large-scalecommercial operations. nia vapors f r varying time intervals by placingAfter exposure and thickening with the ammonia or th papers i a warm(60-80 C.) ammonia gravity amine, the nonwoven material is then driedand cured. oven A fresh 20 p rcent solution of ammonium hy- The dryingstep is normally conducted by passing the droxide was placed in a pan onthe floor of the oven nonwoven material through one or more ovens orheatprior to treating the papers. Immediately after exposure ingchambers maintained at a temperature between t th am i the papers weredried and cured in a about 200 and 325 F. The preferred drying tempera-275 F. air oven for 5 minutes. Physical properties of ture will be inthe range between about 225 and 275 th se cured papers were thendetermined and com- F. The drying ovens may be maintained atsubatmopared against those obtained with identically saturated sphericpressure to facilitate the removal of water if so papers which were notexposed to ammonia. Table I desired. The dried nonwoven is thentypically passed sets forth the test results. through one or more ovensmaintained at higher tem- Tensile (breaking) strengths and elongation ofthe peratures to effect the cure of the binders employed nonwovenmaterial were determined in accordance and develop the ultimate physicalcharacteristics of the with the ASTM D1 1 17-63 Cut-Strip Method.Specinonwoven. Such curing ovens are maintained at temmens for use indetermining the wet tensile strength peratures between about 250 and 325F. preferably were soaked in water at room temperature for 16 hoursbetween 275 and 300 F. In either the drying operation immediately priorto the testing. Solvent tensile or the curing step the nonwoven materialmay be strengths were obtained after immersion of the nonwopassedthrough the heating chamber once or it may be ven in perchloroethylenefor 20 minutes at room temrecycled for as many times as required. Thedrying and perature. Samples (1 inch X 6 inch) of the nonwoven curingneed not be distinct steps, depending on the were sandwiched between two1% inch X 6 inch pieces temperature requirements of the binder it may bedesirof Bondex T-7 tape and sealed with the weight of an able to combinethem in one operation. iron at 275 F. for 30 seconds on a heated plate.The

The following Examples serve to illustrate the invenresistance todelamination for fabrics or internal bond tion more fully; however, theyare not intended to limit strength for papers was then reported as theforce its scope. in these Examples all parts and percentages(ounces/inch) required to peel the tapes apart when are given on aweight basis unless otherwise indicated. pulled at a rate of 12 inchesper minute.

TABLE 1 Paper Properties Ammonia Exposure Time None 5 Seconds l Minute 3Minutes 60 Minutes Dry Tensile Strength (pounds/inch) 61 2 Wet TensileStrength (pounds/inch) 16 25 32 30 3! 1 Qn. uc. i

v a llaper Properties v Q I v v I Ammonia Exposure Time I i None'. 5Seconds l Minute 3 Minutes 60 Minutes Solvent Tensile Strength(pounds/inch) 37 I I 39 Dry Elongation (9%) '9 9 .lnternalBond Strength(ounces/inch) 20 42 ,39

Reported the average obtained for three samples. Oven maintained at118F. I

Paper's exposed 3 minutes at 178 F. prior to curing, i.e., having anidentical heat history. with the samples exposed for 3 ,minutes in Tablel,.developed only about one-half the internal bond strength of samples.treated with ammonia. In other words, by treating the nonwovenmaterialsimpregnated with acrylate binder latices containing carboxylfunctionality with ammonia vapors, l have been able to obtain nonwovenmaterials having twice the resistance to delamination asconventionalsaturated nonwovens. t t I Q f When the abovelatex wasusedto saturate a nonwoven polyester fabric andthe saturated polyester curedfor 5 minutes at 275 C.,the unexposedpolyester had a resistance todelamination of 21 ounces/inch. The polyester sample which was exposedto ammonia for 3 lamination, in fact,. ,the cohesion within thepolyester was greater than the adhesion of the Bondex Tape to thepolyestersaturated fabric and. the fabric pulled. 30

' ple l and diluted to 25' percent total solids-was used to saturate 10mil flat papers. The procedures employed for saturation and testing wereidentical to those previ-.

ously described T-he-papers were exposed to dietl'iylpercent T'.S. )ofExample lll containing about 1 part minutes prior to the cure had agreater resistance to deaminevapors from a 10 percent aqueoussolutionof-the amine for:3' .minutesand 10 minutes prior to the standard275 -,F. cure'for 5 minutes. Internal bond strengths are reported-inTable II and compared withthose 'obtained without exposureto-diethylamine and an unsaturated -paper,control.-,1;

" "TABLEII" Paper Sample J Internal Bond Strength Unsaturated Control- I-5 Unexposed to diethylamine Saturated Control Unexposed 20 todiethylamine 3 minute exposure to 32 diethylamine 10 minute exposure to34 diethylamine 7 EXAMPLE III I 'trile and N-methylol acrylamide. Thepolymer latex I after dilution with water to about 25 percent totalsolids was-used as a saturant for paper samples in accors/inch'andinternal bond strengths of l4 ounces/inch. The paper samples which wereexposed for 3 minutes in an ammonia oven after saturation and before thecureshowed a 10 percent increase in wet tensile strengths and overpercent increase in the internal bond strengths. The internal bondstrength was 22 ounces/inch- EXAMPLE IV About 100' partsof the acrylatepolymer latex (25 interpolymerized acrylic acid was blended with 2.5parts of a water-soluble salt of a copolymer of about 70 percentalkylacrylates and about '30 percent methacrylic acid to'increase the overallc'arboxyl content of the resulting latex. After 3 minutes exposure toammonia at 178F. and curing at 275 F..for 5'minut'es the wet breakingstrength and internal bond strengths were 34. pounds/inch and 35ounces/inch respectively.

Theiabove Examples illustrate the utility of the present process clearlyshowing the nonwoven materials saturated with the carboxyl-containingalkyl acrylate polymer latices and exposed to ammonia or amine vaporshave markedly improved internal bond strengths or resistance todelamination and also improved wet tensile strengths. Thatthe presentprocess is applicable to both papers and nonwoven fabrics is also shown.The

process is-especially attractive in that only short exposure ,toammoniaor amine will renderthese improvements. it is demonstrated that theexposure tov ammonia or 'amine is critical :to obtain the improvedproperties.

The Examples demonstrate'that the present process dance with theprocedure described in Example I. The I saturated unexposed controlpapers cured for 5 minutes at275 F. had wet breaking strengths of 27poundmay be employed with alkyl acrylate binder latices containing'chemicallyboundcarboxyl functionality or alkyl acrylate latex binderswhich are blended with other carboxyl-containing latices to achieve thecarboxyl functionality.

' strength in paper and nonwoven fabric comprising (1 impregnating anonwoven web with an aqueous carboxyl-containing alkyl acrylatecopolymer latex, said copolymer consisting essentially of from about 50to 99.95 percent by weight of (a) one or more esters of ana,B-olefinically unsaturated carboxylic acid having the structuralformula wherein R is hydrogen or methyl and R is a hydrocarbon radicalcontaining from one to 12 carbon atoms polymerized, with up to about 40percent by weight (b) of one ormore copolymerizable vinylidene monomershaving at least one terminal HZIC groupand being free of amine groupsand (c a,B-olefinically unsaturated carboxylic acids containing fromthree to 10 carbon atoms to provide about 0.05 percent to about 25percent by weight of carboxyl groups, said latex containing up to about6 percent by weight, based on the total weight of monomers, ofemulsifiers selected from the group consisting of anionic or nonionicemulsifiers; (2) reacting the impregnated nonwoven web with ammonia oran aliphatic monoamine containing from one to six carbon atoms, at atemperature less than 212 F., for about 1 second to less than 80minutes; and (3) heating the impregnated nonwoven web at a temperaturebetween about 200 and 325 F.

. 2. A process of claim 1 wherein R is an alkyl radical containing twoto eight carbon atoms, in (b) the vinylidene comonomer is selected fromthe group consiting of a vinyl aromatic, a vinyl or vinylidene halide, avinyl ester, an a,B-unsaturated nitrile, and an :,B-unsaturated amide,and (c) is selected from the group consisting of acrylic and methacrylicacids, in amounts of about 0.1 percent to about percent by weight ofcarboxyl groups.

3. A process of claim 2 wherein the latex is maintained at a pH below7.5 during impregnation, in (2) the reaction time is from about 2seconds to less than 5 minutes and in (3) the heating temperature isbetween 200 and 300 F.

4. A process of claim 3 wherein R is an alkyl radical containing fromfour to eight carbon atoms, present in (a) in amount from about topercent by weight and about 5 to 29 percent by weight of (b) vinylidenemonomer. 5. A process of claim 4 wherein (b) is at least one ofacrylonitrile, methacrylonitrile, acrylamide, methacrylamide andN-methylol acrylamide.

6. A process of claim 3 wherein in (a) there is greater than 70 percentby weight of ethyl acrylate, and (b) is about 0.5 to 10 percent ofacrylonitrile and 0.5 to 15 percent weight total of acrylamide,methacrylarnide and N-methylol acrylamide.

7. A process of claim 1 wherein the copolymer contains about 0.1 to 10percent by weight of a,B-olefinically unsaturated carboxylic acid ispolymerized in the presence of the base polymer containing from about 50to 99.9 percent by weight of (a).

methylol acrylamide.

2. A process of claim 1 wherein R1 is an alkyl radical containing two toeight carbon atoms, in (b) the vinylidene comonomer is selected from thegroup consiting of a vinyl aromatic, a vinyl or vinylidene halide, avinyl ester, an Alpha , Beta -unsaturated nitrile, and an Alpha , Beta-unsaturated amide, and (c) is selected from the group consisting ofacrylic and methacrylic acids, in amounts of about 0.1 percent to about10 percent by weight of carboxyl groups.
 3. A process of claim 2 whereinthe latex is maintained at a pH below 7.5 during impregnation, in (2)the reaction time is from about 2 seconds to less than 5 minutes and in(3) the heating temperature is between 200* and 300* F.
 4. A process ofclaim 3 wherein R1 is an alkyl radical containing from four to eightcarbon atoms, present in (a) in amount from about 70 to 95 percent byweight and about 5 to 29 percent by weight of (b) vinylidene monomer. 5.A process of claim 4 wherein (b) is at least one of acrylonitrile,methacrylonitrile, acrylamide, methacrylamide and N-methylol acrylamide.6. A process of claim 3 wherein in (a) there is greater than 70 percentby weight of ethyl acrylate, and (b) is about 0.5 to 10 percent ofacrylonitrile and 0.5 to 15 percent weight total of acrylamide,methacrylamide and N-methylol acrylamide.
 7. A process of claim 1wherein the copolymer contains about 0.1 to 10 percent by weight ofAlpha , Beta -olefinically unsaturated carboxylic acid is polymerized inthe presence of the base polymer containing from about 50 to 99.9percent by weight of (a).
 8. A process of claim 7 wherein the carboxylicacid is acrylic or methacrylic acid and the base copolymer contains 70to 95 percent by weight of (a) wherein R1 contains two to eight carbonatoms.
 9. A process of claim 8 wherein (b) is at least oneacrylonitrile, methacrylonitrile, acrylamide, methacrylamide andN-methylol acrylamide.
 10. A process of claim 9 wherein in (a) R1 isethyl, and (b) is about 0.5 to 15 percent by weight of N-methylolacrylamide.